Fan containment structure having contoured shroud for optimized tip clearance

Abstract

An abradable fan containment structure within a fan section of a turbofan engine is provided. The fan section of the turbofan engine has fan blades and an abradable fan shroud. The abradable fan shroud includes an inner fan casing circumscribing the fan blades such that the inner annular surface of the fan shroud is disposed adjacent the blade tips of the fan blades within the fan section. The inner annular surface is formed from an abradable material. The abradable material contour is substantially triangular along the axial length from the leading edge to the trailing edge. The abradable material has a contoured surface characterized by a trapezoidal shape after being worn when rubbed by the tips of the fan blades during operation of the engine.

What is claimed is: 
     
       1. A fan containment structure comprising: an annular inner fan casing having a leading edge and a trailing edge with an inner annular surface therebetween, the inner annular surface being formed of an abradable material, the inner annular surface of the abradable material having a contour that has at least two different linear slopes in opposite directions located substantially in the forward two-thirds of the inner annular surface. 
     
     
       2. The fan containment structure of claim 1 wherein, the abradable material further comprises a contoured surface characterized by a substantially trapezoidal shape. 
     
     
       3. The fan containment structure of claim 1 further comprising, an outer fan casing attached to the inner fan casing, the outer fan casing being surrounded by a kevlar cover. 
     
     
       4. The fan containment structure of claim 1 wherein, the abradable material is bonded to the inner fan casing by an adhesive layer. 
     
     
       5. The fan containment structure of claim 4 wherein, inner fan casing includes an inner annular groove containing the abradable material. 
     
     
       6. A fan containment structure comprising: an annular inner fan casing with a leading edge, a trailing edge, and having an inner annular surface, the inner annular surface being formed of an abradable material, the inner annular surface of the abradable material having a contour that has at least two different linear slopes in opposite directions between the leading edge and the trailing edge wherein, the abradable material further comprises a contoured surface characterized by a substantially triangular shape. 
     
     
       7. The abradable fan containment structure of claim 6 wherein, the abradable material is bonded to the casing member by an adhesive layer. 
     
     
       8. An abradable fan containment structure within a fan section of a turbofan engine, the fan section of the turbofan engine having fan blades with blade tips and an abradable fan shroud, the abradable shroud assembly comprising: an inner fan casing including an abradable material, the abradable material having an inner annular surface that is substantially triangular in cross-section along the axial length, the inner fan casing circumscribing the fan blades and the inner annular surface being disposed adjacent to the blade tips of the fan blades within the fan section wherein, the abradable material further comprises a contoured surface characterized by a substantially trapezoidal shape during operation of the engine. 
     
     
       9. The fan containment structure of claim 1 wherein, the contour of the inner annular surface is characterized by a substantially triangular shape.